The James Hargest College pupil was picked up by his stepfather at lunchtime on 13 March last year - in breach of a parenting order.

Eleven days later, police found tyre tracks and an oil slick near Curio Bay in the Catlins, which was later confirmed to be the wreckage of Mr Beckenridge's Volkswagen.

But no bodies were found in the car.

Paragon Investigations private investigator Ron McQuilter believes the stepfather and son could still be alive. He has been following the case for the past year and says Mr Beckenridge had five aliases and access to several passports.

He had previously worked on cases where people were thought to have committed suicide, but had been found in motel rooms.

Another case involved a man who ran off with a baby and managed to escape authorities for several months before being found.

Acting detective senior sergeant Stu Harvey said the missing persons case remained open, and police were still treating it as a criminal investigation.

Mr Harvey said a small team of police were still actively working on the case, and they were hopeful the pair were still alive; despite no confirmed sightings of the father and son since 17 March last year.

"Mike's mother has always hoped he is alive and as far as I am aware that has continued till this day and our investigative staff are hopeful as well, but we're keeping an open mind."

Police attach black floats to the car wreck in preparation for its removal from the bay. Photo: RNZ / Ian Telfer

Police will continue to look into any information they receive, even if the case is referred to the coroner, he said.

Police had interviewed a lot of people, including friends of John Beckenridge and had no indication anyone had helped the pair stage their disappearance, Mr Harvey said.